Design studies of membrane permeator processes for gas separation

The intrinsic behaviour of several single-stage and multi-stage permeator systems has been studied using a recently developed algebraic design model. Upper and lower bounds with respect to product purity and recovery in single-stage systems are presented. It is shown that single-stage permeators without recycle can exhibit maxima in permeate purity as a function of the pressure ratio across the membrane. It is illustrated why bypass configurations may be economically profitable in single-stage systems. The effect of product recycle in single-stage systems has been studied. It is shown that permeate recycle can reduce the compressor load in single-stage permeator systems. Similar benefits of retentate recycle have not been identified. The characteristic behaviour of multi-stage systems has been studied. Based on general design criteria, various module configurations have been classified as suitable for recovery of either the slowest or the fastest permeating component. The effect of using different membrane materials at each stage of a multi-stage permeator cascade has been studied. It is shown that improvements with respect to product recovery can be achieved.